1. Field of the Invention
The present invention relates to information playback apparatus that plays back information on pictures, sound, data, and the like.
2. Description of the Related Art
In an information playback apparatus that plays back information signals recorded as slanted tracks on the tape of a video tape recorder or the like, helical scanning is usually performed with rotating heads. In this case, a tracking control is necessary to control the trace positions of the heads so that the heads accurately retrace each track. As a method of the tracking control, a technique called ATF (Automatic Track Finding) is well known. For example, two kinds of pilot signals having different frequencies are multiplexed with a data signal and recorded on the tracks of the tape. An example of tracking control using these pilot signals is disclosed in U.S. pat. appl. Ser. No. 08/040983.
In such an information playback apparatus, when starting playback, a pull-in operation for tracking control is required. If the transient response time for completion of a pull-in is long, the operational responsiveness of the apparatus becomes deteriorated. In prior information playback apparatus using pilot signals, two kinds of zero-crossing points appear in the tracking error detection characteristics, each having a different polarity from the other. Tracking control is stable at one of these two zero-crossing points, but unstable at the other. Therefore, if the pull-in operation is started near an unstable zero-crossing point, it is completed when a stable zero-crossing point is reached. Therefore, there has been a problem in that a long time is required for completion of the pull-in operation.
Further, in the above example, the playback phase of the tape is corrected based on track numbers recorded on the tape, so that the phase of a played-back frame is synchronized with a reference frame phase. However, since a pull-in for tracking control requires some time, there has been another problem in that a long time is required for completion of synchronizing the frame phase.